korrosionsbestendigt weldable martensitiskt stole and still for framstellning of the same

摘要

The invention relates to the field of metallurgy and especially to the preparation of stainless weldable martensitic steel, essentially containing 0.06-0.10 wt-% of carbon, 15.1-16.5 wt-% of chromium, 3.5-4.45 wt-% of nickel, 0.10-0.60 wt-% of silicon, 0.20-0.50 wt-% of manganese, 0.25-0.40 wt-% of niobium and/or 0.05-0.20 wt- % of zirconium. It also contains at least one element chosen from the group of yttrium, cerium and lanthanum, in an amount of 0.05-0.20, 0.05-0.15 and 0.05-0.15 wt-%, respectively. The steel in question also comprises at most 0.025 wt-% of phosphorus, at most 0.02 wt-% of sulphur and at most 0.20 wt-% of copper. The rest of the material is essentially iron and unavoidable impurities in the form of non-ferrous metals. In the process for the production of this steel, the material with the above composition is melted, the molten metal is placed in a mould, where it is allowed to solidify, after which the ingot formed is cooled. The cooling is carried out in at least two stages. In the first one, the ingot is cooled to a temperature that lies within the range of the martensitic transformation but is not below 100 degrees C. This is followed immediately by heating the steel to an annealing temperature of 600-650 degrees C. In the next stage, the ingot is cooled to the martensitic transformation temperature but to a level that is at least 50 degrees C lower than the cooling temperature in the previous stage. As a result of this multi-stage cooling process, the temperature of the ingot is reduced to a value that lies below the final temperature of martensitic transformation. The final annealing step is carried out in the range of 600-650 degrees C, followed by cooling to room temperature. IMAGE